Abstract: LBB (Leak-Before-Break) is an important analysis method for insuring the structure safety and reliability of nuclear reactor. It must consider the affection of fatigue and creep to the crack growth for the nuclear pipes in the high temperature reactors (as fast reactor) beyond the creep temperature. The paper summarizes a set of LBB method applying for the safe analysis of the nuclear pipes beyond the creep temperature, basing on A16 in the France RCC-MR standard and carrying on LBB analysis for a section of pipe in the heat drainage system in fast reactor. By calculation, creep affects the crack growth greatly beyond the creep temperature. It is demonstrated that the pipe meets the conditions that the crack is stable and the leakage is detectible which LBB asks for, and it also satisfies the time request from the beginning of leak to the moment at which the crack is unstable.